1. Field of the Invention
The present invention relates to the field of display, and in particular to an organic light emitting diode (OLED) display and a source driver.
2. The Related Arts
The organic light-emitting diode (OLED) display has the advantages of active light-emitting, low driving voltage, high light-emitting efficiency, short response time, high clarity and high contrast, near 180°, wide operation temperature range, and the ability to realize flexible display and large-size full-color display, and is often considered as the technology with most potential.
The OLED usually comprises: an anode, an organic light-emitting layer disposed at the anode, an electron transmission layer disposed at the organic light-emitting layer, and a cathode disposed at the electron transmission layer. The known OLED is mostly driven by direct current (DC), and emitting the hole from the anode and electron from the cathode to the organic light-emitting layer when operating. The electrons and holes combination generates the excited electron-hole pair, and transform the excited electron-hole pair from the excited state to the basic state to emit light.
FIG. 1 shows a pixel driver commonly used for a known OLED display, which comprises: a first thin film transistor (TFT) T1, a second TFT T2, and a capacitor C, i.e., 2T1C pixel driver; the first TFT T1 has the gate connected to a scan signal Gate, the drain connected to a data signal Data, and the source connected to the gate of the second TFT T2 and one end of the capacitor C; the second TFT T2 has the drain connected to positive power source OVDD, and the source connected to the anode of the OLED D; the cathode of OLED D is connected to the negative power source OVSS; the other end of the capacitor C is grounded. When the gate driver provides the scan signal Gate to the pixel, the source driver provides the data signal Date to charge the capacitor C. The voltage of the capacitor C is used as the gate voltage for the second TFT T2 to control the current flowing through the OLED. Usually, when the OLED display employing the above pixel driver operates, all the pixels keep emitting light. As the usage time increase, the hole and the electrons accumulate the respective interface between transmission layer and the light-emitting layer to form built-in electric field inside the OLED and increase the threshold voltage of the OLED to reduce the luminance.
To solve the above problem, the known technology improves the above pixel driver. Refer to FIG. 2, the improved the pixel driver comprises: a first TFT T1, a second TFT T2, a third TFT T3, a fourth TFT T4 and a capacitor C. The first TFT T1 has the gate connected to the scan signal Gate, the drain connected to the source of third TFT T3, the source connected to the first node Q; the second TFT T2 has the gate connected to the first node Q, the drain connected to the cathode of OLED D, the source grounded; the third TFT T3 has the gate connected to one of the first light-emitting control signal G and the second light-emitting control signal SG, the drain connected to the data signal Data; the fourth TFT T4 has the gate connected to the other one of the first light-emitting control signal G and the second light-emitting control signal SG, the drain connected to the first node Q; the source grounded; the capacitor has one end connected to the first node Q, and the other grounded. For the pixel using the above pixel driver, when the gate of third TFT T3 of the pixel driver for one of the pixels is connected to the first light-emitting control signal G and the gate of fourth TFT T4 is connected to the second light-emitting control signal SG, the pixel drivers for the four adjacent pixels (above, below, left and right) have the gates of third TFTs T3 connected to the second light-emitting control signal SG, and the gate of fourth TFT T4 is connected to the first light-emitting control signal G. Refer to FIG. 3, the first light-emitting control signal G switches constantly between the high and low levels with a period of a frame, and the second light-emitting control signal SG is the inverted signal for the first light-emitting control signal G. Through the improved pixel driver, the adjacent pixels emit light alternatingly to shorten the light-emitting time to reduce the ageing of OLED display. However, the above improvement adds two TFTs, which leads to a smaller opening ratio of the OLED display, as well as two control signals, which increases the cost for the driver system.